Osteoarthritis is the most common disorder of the synovial joint, causing pain and disability in an estimated 12 percent of Americans age 25 and older and 30% of those over 60. The most widely used treatments are analgesic medications to relieve pain symptoms and ultimately, joint replacement. The OsteoArthritis Initiative (OAI) was established in 2000 as a knee health study to establish and maintain a natural history database for osteoarthritis that includes clinical evaluation data, radiological (x-ray and magnetic resonance) images, and a biospecimen repository from 4796 men and women ages 45-79 enrolled between February 2004 and May 2006. At present there are no laboratory tests to help make or confirm an OA diagnosis, predict the progression of OA or determine whether therapies may be altering the course of the disease. The field of biomarkers for OA is relatively new, and recently developed markers for OA diagnosis and progression are currently being tested. At this point, exciting new results are available on study populations and novel biomarkers have been discovered. Following up on the successful NIAMS/NIA sponsored Biomarkers Network Workshops in 2004, 2005 and 2006, three additional OA Biomarker Workshops are planned over the next four years. They will occur approximately every 18 months and cover the range of current interests in the biomarkers field. "The initial meeting will be a direct continuation of the previous meetings wherein current research on biochemical biomarkers and results of clinical studies using the biomarkers will be reported as well as new validation criteria. " The second OA Biomarker Workshop will highlight the recent exciting advances in the genetics of OA and the use of genome wide screening to identify new targets for biomarkers of disease, risk of disease, and therapeutics. "The third OA Biomarker Workshop will highlight the use of imaging modalities such as X-rays, MRI and other imaging techniques as biomarkers for OA. A Website will be established that highlights information related to biomarkers. In many other fields of medicine, in particular cancer, biomarkers have become the gold standard in the diagnosis and analysis of progression of disease. With OA having such a high impact on our society, it is critical that valid biomarkers be developed that will allow proper planning of treatment of the disease and encourage the development of disease-modifying drugs.